AbstractThis study examined the role of the thymus in hypertension. Seven to eight week old, normotensive Wistar-Kyoto rats (WKYs) (systolic blood pressure 138±7 mm Hg) received a bolus injection of (1) WKY thymic extract (control), (2) spontaneously hypertensive rat (SHR) thymic extract, (3) SHR liver extract or (4) normotensive Sprague-Dawley rat (SD) thymic extract. Blood pressures of WKYs receiving SHR thymic rose significantly (p<0.01) over an eight week period (168±6 mm Hg), while WKYs injected with WKY thymic extract (143±10), SHR liver extract (144±5) or SD thymic extract (138±4) showed no change in blood pressure. Thymuses from WKYs injected with SHR extract were significantly (p<0.01) smaller than thymuses from WKYs injected with WKY extract. Aorta from WKYs administered SHR extract were significantly (p<0.01) hyperresponsive to contractile agents, suggesting that immune dysfunction may lead to vascular damage as seen in several hypertensive models. The results suggest that hypertension can be transferred via an endogenous thymic factor, possibly a viral pathogen.